The L550 intermediate of bacteriorhodopsin (bR) has drawn much attention with respect to the mechanism of light-driven proton transport because it releases the Schiff base (SB) proton in the L > M transition. Two different conformations have been suggested for the retinal chromophore in the L intermediate and these correspond to different orientations of the SB proton in the transport pathway. To date solid state NMR techniques have been proven powerful probes of other states of bR. In order to extend similar studies to the L intermediate, we focused on the Schiff base (SB) nitrogen by monitoring the 15N chemical shift in [e-15N]Lys-bR under conditions that stabilize the L intermediate. Upon illumination at low temperatures (as low as -130 ~C) with light of >610 nm, a new SB signal is detected in the 15N NMR spectrum which disappears upon thermal relaxation at -80~C. The signal is in the range for a protonated SB but about 18 ppm downfield from bR568 and 12 ppm downfield from bR555. Comparison with the 15N chemical shifts of model compounds, particularly 6-s-trans-13-cis protonated Schiff bases (pSB) of retinal, suggests that the H-bonding of the SB with its counterion is significantly stronger in L intermediate than in bR555 (which in turn is stronger than in bR568). The dissimilarity of the 15N chemical shifts of bR555 and L550 occur inspite of the similarity of their visible spectra. Comparison with the model compounds shows that bR555 has a normal relationship between these two parameters and L anomalous. This may be an indication of the proposed distortion of the polyene system in L.